There has recently been developed a new x-ray fluorescence technique for determining the amount of lead borne in the skeletons of patients. This technique involves exposing the patient to a quantity of low energy x-rays, and detection and spectral analysis of photons fluoresced from the bone. See Wielopolski et al, "Feasibility of non-invasive analysis of lead in the human tibia by soft x-ray fluorescence," Med. Phys. 10(2), March/April 1983, pp. 248-251. Conveniently, the source and detector are juxtaposed to the tibia of a patient. The patient is seated in a chair with one leg extended forward and held in position The source and detector must be juxtaposed to a tibia at a predetermined angle with respect to one another, typically 90 degrees and at a predetermined spacing from the tibia, such that the amount of photons fluoresced can readily be correlated with those from other patients.
The present invention concerns an apparatus for supporting the source of x-rays and detector in precisely the desired position with respect to the tibia of the patient, such that the measurement can be made.
The x-ray fluorescence method of measurement of skeletal lead burden described above is considered to be a very significant improvement in diagnosis of lead toxicity in children. Lead toxicity is a major health problem in children, so that it is desired to provide x-ray fluorescence testing for large numbers of children in a convenient and expedient manner. To this end, it is desired to outfit a mobile van with a complete test apparatus, including the x-ray source and detector, and associated data processing equipment to analyze the results, so that this can be taken to an industrial site or community center or the like and used to perform the testing where convenient, such that a reasonably complete examination of the community can be anticipated.
To mount x-ray apparatus in a vehicle for such purposes is not a simple task. In particular, the apparatus must be mounted in such a way that it is securely held in a safe position and not damaged during travel of the vehicle from place to place, yet in which it can conveniently be made ready for use when the test site is reached. More particularly, the steps involved in getting the apparatus ready for use at a test site and securing it again for travel at the end of a day's testing must be simple, convenient, and foolproof; otherwise, the securing process will be neglected, and the apparatus eventually damaged in travel.
In order that the source and detector can be properly adjustable with respect to the patient, three degree of freedom of motion along orthogonal axes and two degrees of freedom of rotation of the source and detector with respect to the patient are necessary. These requirements pose very substantial design constraints on the unit. Furthermore, these motions of the apparatus must be either powered or made essentially effortless by design of the gantry apparatus.
At the same time, the unit must be safe. For example, a complete power failure may not permit any portion of the apparatus to fall on the patient. Furthermore, and as noted above, the system must be convenient and foolproof in use and must be manufacturable at a reasonable cost if such testing is to be economically feasible.
The prior art does not teach apparatus which is suitable for such purposes. For example, Miyahara et al U.S. Pat. No. 4,503,552 teaches a "simple mounting structure for dental x-ray apparatus" which appears to provide three degree of freedom and at least one degree of rotation. This structure appears to be far too flimsy and insubstantial to be suitable for use in a vehicle. In particular, no means for securing the unit against vibration and road shock during travel is provided.
U.S. Pat. No. 4,694,481 to Tashjian et al shows a transportable x-ray apparatus, but this device does not appear to provide the full range of motion required by the particular x-ray fluorescence test discussed above. Moreover Tashjian et al does not appear to teach any means for securing the x-ray source and detector for travel, which as will appear below is an important aspect of the present invention.
Finally, U.S. Pat. No. 4,181,347 to Clark shows a mobile computerized tomography (CT) unit. This patent simply indicates that the CT equipment is to be mounted on shock vibration-isolation mounts.